Plural beam mass spectrometer

ABSTRACT

A mass spectometer in which plural beams of ions can be generated simultaneously in separate sources. Convergent deflectors bring the beams close together for passage through an analyzer region. A divergent deflector separates an analyzed beam to provide adequate beam spacing for the positioning of detectors to respectively receive the beams.

United States Patent Green June 19, 11973 PLURAL BEAM MASS SPECTROMETER 3,407,323 10/1968 Hand 250 419 ME 3,573,453 4/1971 Powers..... 250/41,) ME [75] lnvemor- Noel Green Sale England 3,571,642 5 1971 Westcott 250 419 ME [73] Assignee: Associated Electrical industries Llmlted London England Primary Examiner-William F. Lindquist [22] Fil d; S t, 17, 1970 Att0rneyWatts, Hoffmann, Fisher & Heinke [21] Appl. No.: 73,072

[57] ABSTRACT [30] Foreign Application Priority Data Sept 18 1969 Great Britain 46 162/69 A mass spectometer in which plural beams of ions can be generated simultaneously in separate sources. Con- [52] US (125M419 ME 250/419 SE 250/419 D vergent deflectors bring the beams close together for 51 Int. Cl. .j ..1101 j 39/34 Passage through analyzer region [58] Field of Search 250/419 ME, 41.9 D, A divergent deflector separates an analyzed beam to 250/419 SE; 313/63 provide adequate beam spacing for the positioning of detectors to respectively receive the beams. [56] References Cited UNITED STATES PATENTS 15 Claims, 3 Drawing Figures 3,231,736 1/1966 Daly 250/419 D Patented June 19, 1973 3 Sheets-Sheet 1 INVEN'II'OR. BRIAN N. GREEN A rmRA/sm Patented June 19, 1973 3 Sheets-Shea; 2

INVENTOR. BR/AN N. GREEN 3%, Wzmfiik/ fiim ATTORNEYS Patented Juhe 19, 1973 3,740,551

3 sheets-Shoot 5 g 1: u 0 k 3 j 3 [L INVENTOR.

Lu 0 3 BRIAN N. GREEN 0 u 0 1 72410 flm a A T TORN FYS PLURAL BEAM MASS SPECTROMETER Cross Reference to Related Application Plural Beam Mass Spectrometer for Conducting High and Low Resolution Studies, Ser. No. 638,133, now U.S. Pat. No. 3,573,453 filed May 12, 1967 by Patrick Powers.

Beam Correcting Device for Mass Spectrometers and Method of Operation, Ser. No. 39,240, now U.S. Pat. No. 3,657,531 filed May 15, 1970 by Sidney Evans and Reginald Graham.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mass spectrometers and more particularly to a plural beam mass spectrometer in which a plurality of beams can be generated simultaneously and passed concurrently through a common analyzer region.

2. Description of the Prior Art In the analysis of substances with a mass spectometer, ions of a substance being analyzed are generated in an ion source and then emitted from the source as an ion beam. The beam passes through, in the case of a single-focusing mass spectrometer, a magnetic analyzer; and in the case of a double-focusing mass spectometer, an electrostatic analyzer and then a magnetic analyzer.

During a given analytical study, the accelerating voltage of the source or the voltage applied to the magnetic analyzer may be varied to scan the instrument. As the instrument is scanned, ions of different mass/charge ratios are deflected onto the collectors successively and the sample is thus analyzed. 7

In the referenced Powers application, there is a dis closure of, among other things, the use of two ions sources which are capable of simultaneously producing two ion beams. The two beams are passed, in a common ion tube, through a single analyzer system and then collected respectively on each of two collectors. The two beams may be passed through the ion tube either simultaneously, or selectively, one at a time.

The dual beam instrument provides a number of advantages not previously available. Included among these are:

- 1. With prior instruments, high and low resolution studies were conducted sequentially. That is, slit structures, which delineate the thickness of an ion beam reaching the collector and therefore the range of mass number of ions which can simultaneously pass through the slit, are adjusted to define a very small slit when high resolution is desired and a relatively larger slit when low resolution is desired. In the past, one adjusted the slit structure from its high to its low resolution condition, or vice versa, in conducting scans alternately of high and low resolution. With a double-beam instrument, it is possible to simultaneously conduct high and low resolution studies by having the slit structures for one beam in high resolution position and those for the other beam in low resolution position while producing beams from identical samples.

2. Where a reference compound is employed, it is possible to use the reference compound in one 6 to use relatively high amounts of sample. With the sample and reference compound in separate beams, lesser amounts of sample are required, and, in fact, tests have indicated that the amount of sample required may be reduced by as much as a factor of 1,000.

3. It is possible simultaneously to conduct studies of metastable ions and the parent ion where, with prior art techniques, metastable studies were also conducted sequentially with respect to studies of the parent ions.

A problem which is present in a plural beam mass spectrometer is that if two sources are used in side-byside relation, the emitted beams are to far apart for analysis in anything but an extremely large analyzer section. The present invention is directed to a structure which overcomes this problem and produces other advantages as well.

SUMMARY OF THE PRESENT INVENTION With the present invention two or more sources are positioned for emitting plural ion beams simultaneously. Each emitted beam passes through converging deflectors near the source so that the beams are deflected toward one another into close, but spaced, relationship before they enter the analyzers. The beams pass through, in the preferred embodiment, electrostatic and magnetic analyzers of relatively conventional construction.

As the beams emerge. from the analyzers, they are relatively close together. They are, in fact, so close together that it is physically impossible to position two electron multiplier tubes such that each is positioned to receive one of the two beams. With the present invention this problem is overcome through the provision of a divergent deflector which may be referred to as the analyzed beam deflector. The divergent deflector deflects one of the beams away from the other allowing ample room for the positioning of two electron multiplier tubes such that each intercepts one of the beams. The electron multiplier tubes are positioned such that the focal lengths of the beams are identical.

The provision of the divergent deflector produces other advantages as well. For example, it is an electrostatic deflector. Since it is an electrostatic deflector, it functions in a manner comparable to the electrostatic analyzer. This means that, metastable ions are not deflected to the collector, but rather only parent ions or those very close to the mass/charge ratios very close to the parent ions reach the collector. Thus, a metastable study may be collected with a non-deflected beam, while the parent ions are analyzed with the deflection beam without the metastables present, allowing for, in certain circumstances, improved analytical results.

Other advantages of deflecting the two beams into closely spaced relationship include, in addition to the provision of a relatively small and therefore inexpensive magnet;

l. The fields through which the two beams pass in the analyzers have a far greater probability of being identical. This is important because if the fields through which the two beams pass are identical, accurate comparison of the respective spectra can be made.

2. Image defects because of image curvature are relatively small, thus achieving greater sensitivity for a given resolution.

By image curvature it is meant that a beam, as it enters and leaves the magnetic analyzer, is not subjected to uniform magnetic flux throughout its width. Thus, as viewed in a transverse plane of cross section through the beam, ions at the edge of the beam will be subjected to different deflection forces than those at the center of the beam. In a conventional mass spectrometer, this phenomenon is usually ignored by positioning the slits such that the ions which pass the collector are taken from that portion of the beam, transversely speaking, which is central. With two beams traveling in spaced relationship, it is akin to dealing only with ions in a conventional beam that are in portions of the beam adjacent the edges where curvature is the greatest.

Accordingly, another of the features of the present invention is the provision of slit structures which are at an angle with respect to one another other than parallel and which are canted with respect to the plane of deflection in the analyzers. Thus, they are positioned to produce maximum sensitivity for a given resolution by compensating for the beam curvature attendant in a double-beam construction not equipped with curvature compensation of the type described in the abovereferenced Evans et al application.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompa nying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a mass spectrometer partially in section in a plane of deflection of the analyzers;

FIG. 2 is a fragmentary, partially schematic, plan view of a mass spectrometer showing the deflectors of this invention; and,

FIG. 3 is an electrical schematic drawing showing the deflectors of this invention and the circuitry for supplying power to them.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and to FIG. 1 in particular, ion sources are in a source section shown generally at 10. The sources generate plural ion beams which are accelerated by electrodes within the sources through exit slits indicated schematically at 11. After the beams have passed through the exit slits l 1, they pass through a novel source convergent deflector section 13 which will be described in greater detail presently. The convergent deflector brings the beams relatively close together. The beams then pass through an electrostatic analyzer 14 of relatively conventional construction.

After a beam has passed through the electrostatic analyzer 14, it may pass'through an ion current collector l5. Ion collectors are known in the art and the collector 15 may be of known and conventional construction other than for modification to accommodate plural beams. The beam next passes through a magnetic analyzer 16 where it is further deflected. After the beam passes through the magnetic analyzer 16, the beams pass through slit structure shown schematically at 17. The slit structure 17 includes novel construction which will be described in greater detail presently.

After the beams have passed through the slit structure 17, they pass through a divergent deflection section 18. Where there are two beams in the preferred construction, one beam passes through the divergent deflection section without further deflection and the other is deflected outwardly. After traversing the divergent deflection section, the beams enter a collector section 19. In the disclosed embodiment, one collector in the form of an electron multiplier tube 20 is shown in FIG. 1.

Referring now to FIG. 2, a somewhat diagrammatic plan view of a two-source double-beam mass spectrometer is shown. The source section 10 is composed of a pair of ion sources in source housings 25, 26. The source housings 25, 26 define separated chambers 27, 28 respectively. The separated chambers 27, 28 are respectively and individually pumped through exhaust passages 29, 30 to maintain conventional vacuum conditions in the source chambers 27, 28.

Within each source chamber 27, 28 an ion generating source of conventional construction is positioned. Each source may be, for example, a conventional electron bombardment source. On the other hand, one of the features of a plural beam mass spectrometer is that the sources need not be identical. One may provide two types of sources such as electron bombardment and field ionization to provide greater flexibility in conducting studies.

As is clearly indicated by the schematic showing of FIG. 2, ion beams indicated by pairs of dashed lines 32, 33 are emitted from the sources. These beams, as emitted through the exit slit structure 11, are relatively widely spaced. If a study were conducted with the beams so spaced, it will be appreciated that very large electrostatic and magnetic analyzers 14, 16 would be required and particularly the magnetic analyzer would be of large mass and expensive.

One of the outstanding advantages of this invention is provided in the source convergent deflection section 13. In this section, each of the two beams 32, 33 is first deflected to a convergent path so that the beams approach one another and thereafter deflected in the opposite direction to bring the beams back into parallel, but now much more closely spaced, relationship.

The convergent deflecting section is positioned within an evacuated mass spectrometer housing 35. The housing 35 thus envelopes not only, as is known in the art, the electrostatic and magnetic analyzers and collectors but also the convergent and divergent deflector sections.

The convergent deflector section has two pairs of oppositely charged convergent sectors 36, 37 and 38, 39. The convergent sectors 36, 37 deflect the beam 32 toward the beam 33; and, conversely, the sectors 38, 39 deflect the beam 33 toward the beam 32. It will be seen that faces 36 A39A of the sectors of each pair are arcuately curved, defining segments of cylinders of common curvature. The curvature of these faces is equivalent to the curvature of the beams 32, 33 as they pass through their respective and associated convergent sectors.

The beams next pass through spaces delineated by a central common sector 40 and parallel path-producing sectors 41, 42, respectively. The sectors 41, 42 are 0ppositely charged so that the beams are oppositely deflected, through an angle of curvature corresponding to the curvature produced in the convergent sectors, to bring the beams back into parallel but closer relationship.

The sectors 40-42 also have arcuately curved faces that are segments of cylinders. Thus, the common segment has a face 40A which is concentric to a face 41A and a face 403 which is concentric to a face 42A. These faces have curvatures corresponding to the desired curvature of the beam in the plane of FIG. 2 and equal and opposite to the curvature of the convergent sectors.

In mass spectrometry, since the molecules from which the ions are formed have random thermal velocity in the ion source, ions commonly have a small component of velocity in a direction that is in the plane of the drawing of FIG. 2. Therefore, to prevent any intermixing of the beams 32, 33, a collimating slit structure 45 is provided. Collimating slit structure 45 respectively has collimating slit apertures 46, 47 for the beams 32, 33.

The deflected and collimated beams 32, 33 traverse through a common ion tube, a portion of which is shown at 50. While in the tube, they pass through the electrostatic and magnetic analyzers 14, 16 and thence through the collector slit structure 17. As has been indicated previously, the magnetic analyzer causes ion beam curvature. Accordingly, the slit structure 17 has slit openings 51, 52 which are canted with respect to the plane of analyzer deflection, i.e. the plane of FIG. 1, and are in non-parallel relationship with one another. After the beam 32 has passed through the slit 51, it proceeds, without further deflection, to the electron multiplier 20. Since the beams are too close together to permit another electron multiplier 52 to be positioned in the path of the beam 33, the beam 33 is deflected outwardly in the divergence or deflector collector section 18.

The divergence collector section diverts the beam 33, after it has been analyzed by the analyzers 14, 16, away from the beam 32. It is composed of electrically charged sectors 54, 55. These sectors, like the sectors in the convergence region 15, have arcuately curved surfaces 54A, 55A each of which defines a segment of a cylinder. The curvature of the surface 54A, 55A is, again, a curvature corresponding to the desired beam deflection curvature.

It will be appreciated that both beams can be deflected, but for simplicity of manufacture and to permit the metastable studies described above, the deflection of one of the two beams is preferred.

The instrument is constructed such that the total lengths of the path of travel of the two beams 32, 33, and therefore the focal lengths of the respective beams, are identical from their respective sources to their respective collectors. This permits precise comparative analysis of the two beams which have been analyzed is identical conditions.

In FIG. 3, a suitable method of deriving appropriate voltages for the various deflection sectors is shown. An array of fixed and variable resistors R1-R14 is connected across an accelerated beam voltage supply 60. Suitable voltages are tapped from the array of resistors to give appropriate relative potentials between the ion sources 25, 26 and the sectors of the regions 13, 18.

The resistors R1 and R2 are preferably such that a major portion of the voltage from the accelerating voltage supply 60 appears across R1, for example a positive voltage of 4,000 volts, and a minor portion appears across resistor R2, for example a negative voltage of 200 volts. The potentials for the sectors of the deflection regions are preferably arranged to be substantially equal and positive and negative with respect to ground. Suitable potentials for the sectors of the convergent regions 13 are plus and minus volts and for the sectors of the divergent deflector plus and minus 60 volts. The potentials of at least one sector of each pair are preferably adjustable as shown in FIG. 3 by means of variable resistors R6, R7, R12, R13, R14. The variable resistors are provided to allow for setting up the mass spectrometer for operation and to compensate for any errors in the manufacture of a spectrometer.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A mass spectrometer comprising:

a. a plurality of spaced ion sources each for generating and emitting a beam of ions along a path of ion travel;

b. an analyzer for deflecting generated beams of ions and separating ions of a beam according to the mass/charge ratios of the ions; I

c. a pair of ion sensitive structures positioned in spaced relationship and to receive ions from a beam deflected by the analyzer;

. source beam deflection means interposed between at least one ion source and the analyzer for deflection ions emitted by the one source along a path paralleling the paths of ions emitted from another source with the two paths after deflection being closer to one another than locations in said one and said another sources where ions are generated; and,

e. analyzed beam deflection means between said analyzer and said structures to deflect certain of the ions of a beam onto one of the structures while other of the ions pass to the other structure.

2. The mass spectrometer of claim I wherein the focal length of a beam of ions traveling from the source to the one structure is substantially equal to the focal length of a beam from the source to the other structure.

3. The mass spectrometer of claim I wherein said source deflection means deflects ions in a plane transverse to the plane of analyzer deflection.

4. The mass spectrometer of claim 1 wherein said analyzed beam deflection means deflects ions in a plane transverse to the plane of analyzer deflection.

5. The mass spectrometer of claim I wherein said source deflection means is constructed for deflecting the beam emitted by the one source toward the paths of a beam from said another source prior to deflecting the beam parallel to the path of said another ions.

6. The mass spectrometer of claim 1 wherein the source deflection means is adapted to deflect both beams toward one another and thereafter along parallel paths.

7. The mass spectrometer of claim 6 wherein said source beam deflection means comprises:

first electrostatic deflector means adapted to deflect each of said two beams toward the other of said two beams; and,

second electrostatic deflector means adapted to deflect each of said two beamsalong parallel paths.

8. The mass spectrometer of claim 7 wherein each of said electrostatic deflector means comprises arcuately shaped electrostatic deflector plates.

9. The mass spectrometer of claim 8 wherein:

said first electrostatic deflector means comprises two pairs of spaced arcuately shaped deflector plates, each pair being adapted to receive one of said two beams between its plates and to deflect the beam toward the other of said two beams; and,

said second electrostatic deflector means comprises a doubly arcuate-shaped center plate and a pair of arcuate-shaped deflector plates spaced from said center plate, each of said two beams being received between said center plate and a separate one of said outer plates for deflection into parallel paths.

10. The mass spectrometer of claim 7 wherein said analyzed beam deflector means comprises a pair of arcuate-shaped deflector plates adapted to receive one of said two beams and to deflect the beam toward said one structure.

11. The structure of claim 1 wherein beams of ions emitted by both said one and said other sources are deflected by said source deflection means.

12. A mass spectrometer comprising:

a. a pair of spaced ion.sources each for generating and emitting a beam of ions of like polarity along a path of ion travel;

b. an analyzer for deflecting generated beams of ions and separating ions of each beam according to the mass/charge ratios of the ions;

c. source beam deflection means interposed between at least one ion source and the analyzer for deflecting ions emitted by the one source along a path paralleling the paths of ions emitted from another source with the two paths after deflection being closer to one another than locations in said one and said another sources where ions are generated;

d. a pair of ion sensitive structures positioned in spaced relationship, one of the structures being positioned to receive ions from one of the beams deflected by the analyzer and the other structure being positioned to receive ions of the other beam; and,

e. analyzed beam deflection means between said analyzer and said structures to deflect the ions of said one beam onto said one structure while ions of said other beam travel to said other structure.

13. The mass spectrometer of claim 12 wherein said source deflection means deflects ions in a plane transverse to the plane of analyzer deflection.

14. The mass spectrometer of claim 13 wherein the focal length of a beam of ions traveling from said one source to said one structure is substantially equal to the focal length of the beam from said other source to said other structure.

15. The mass spectrometer of claim 12 wherein said analyzed beam deflection means deflects ions in a plane transverse to the plane of analyzer deflection. 

1. A mass spectrometer comprising: a. a plurality of spaced ion sources each for generating and emitting a beam of ions along a path of ion travel; b. an analyzer for deflecting generated beams of ions and separating ions of a beam according to the mass/charge ratios of the ions; c. a pair of ion sensitive structures positioned in spaced relationship and to receive ions from a beam deflected by the analyzer; d. source beam deflection means interposed between at least one ion source and the analyzer for deflection ions emitted by the one source along a path paralleling the paths of ions emitted from another source with the two paths after deflection being closer to one another than locations in said one and said another sources where ions are generated; and, e. analyzed beam deflection means between said analyzer and said structures to deflect certain of the ions of a beam onto one of the structures while other of the ions pass to the other structure.
 2. The mass spectrometer of claim 1 wherein the focal length of a beam of ions traveling from the source to the one structure is substantially equal to the focal length of a beam from the source to the other structure.
 3. The mass spectrometer of claim 1 wherein said source deflection means deflects ions in a plane transverse to the plane of analyzer deflection.
 4. The mass spectrometer of claim 1 wherein said analyzed beam deflection means deflects ions in a plane transverse to the plane of analyzer deflection.
 5. The mass spectrometer of claim 1 wherein Said source deflection means is constructed for deflecting the beam emitted by the one source toward the paths of a beam from said another source prior to deflecting the beam parallel to the path of said another ions.
 6. The mass spectrometer of claim 1 wherein the source deflection means is adapted to deflect both beams toward one another and thereafter along parallel paths.
 7. The mass spectrometer of claim 6 wherein said source beam deflection means comprises: first electrostatic deflector means adapted to deflect each of said two beams toward the other of said two beams; and, second electrostatic deflector means adapted to deflect each of said two beams along parallel paths.
 8. The mass spectrometer of claim 7 wherein each of said electrostatic deflector means comprises arcuately shaped electrostatic deflector plates.
 9. The mass spectrometer of claim 8 wherein: said first electrostatic deflector means comprises two pairs of spaced arcuately shaped deflector plates, each pair being adapted to receive one of said two beams between its plates and to deflect the beam toward the other of said two beams; and, said second electrostatic deflector means comprises a doubly arcuate-shaped center plate and a pair of arcuate-shaped deflector plates spaced from said center plate, each of said two beams being received between said center plate and a separate one of said outer plates for deflection into parallel paths.
 10. The mass spectrometer of claim 7 wherein said analyzed beam deflector means comprises a pair of arcuate-shaped deflector plates adapted to receive one of said two beams and to deflect the beam toward said one structure.
 11. The structure of claim 1 wherein beams of ions emitted by both said one and said other sources are deflected by said source deflection means.
 12. A mass spectrometer comprising: a. a pair of spaced ion sources each for generating and emitting a beam of ions of like polarity along a path of ion travel; b. an analyzer for deflecting generated beams of ions and separating ions of each beam according to the mass/charge ratios of the ions; c. source beam deflection means interposed between at least one ion source and the analyzer for deflecting ions emitted by the one source along a path paralleling the paths of ions emitted from another source with the two paths after deflection being closer to one another than locations in said one and said another sources where ions are generated; d. a pair of ion sensitive structures positioned in spaced relationship, one of the structures being positioned to receive ions from one of the beams deflected by the analyzer and the other structure being positioned to receive ions of the other beam; and, e. analyzed beam deflection means between said analyzer and said structures to deflect the ions of said one beam onto said one structure while ions of said other beam travel to said other structure.
 13. The mass spectrometer of claim 12 wherein said source deflection means deflects ions in a plane transverse to the plane of analyzer deflection.
 14. The mass spectrometer of claim 13 wherein the focal length of a beam of ions traveling from said one source to said one structure is substantially equal to the focal length of the beam from said other source to said other structure.
 15. The mass spectrometer of claim 12 wherein said analyzed beam deflection means deflects ions in a plane transverse to the plane of analyzer deflection. 